The present invention relates to a shift control system for an automatic transmission, and more particularly to a shift control system which suitably executes an interchange shift by engaging a first friction element of a plurality of friction element and by disengaging a second friction element of the friction elements after a pressure signal relating to an operation pressure of the first friction element is generated.
In order to realize a further smooth shift feeling during an interchange shift of an automatic transmission, various shift control systems for automatic transmissions have been proposed.
However, there is a demand to further improve an interchange shift of an automatic transmission.
It is therefore an object of the present invention to provide a shift control system which enables an interchange shift to be smoothly executed while suppressing the generation of shift shocks.
A shift control system according to the present invention is for an automatic transmission comprises a first friction element engaged by increasing a first oil pressure supplied to the first friction element and a second friction element disengaged by decreasing a second oil pressure supplied to the second friction element in response to a pressure signal of the first oil pressure. An interchange shift of the automatic transmission is executed by interchanging engagement conditions of the first and second friction elements. The shift control system comprises a controller which is arranged to decrease the second oil pressure of the second friction element by a second predetermined gradient after a loss stroke of the first friction element is terminated, to increase the first oil pressure of the first friction element by a first predetermined gradient after the loss stroke of the first friction element is terminated, and to determine the first gradient such that a difference between a command pressure and an actual pressure of the first friction element is kept substantially constant.